The present invention relates generally to a conveyor system for moving webs or sheets of material with maximum efficiency, with minimum power requirements and with minimal chatter, vibration and deflection. The system is especially suitable for photographic developing equipment.
Machines are known which utilize an extended transport roller system for carrying flexible workpieces, such as photographic films or papers. Typical of such machines are those used to develop photographic films. These utilize a series of treatment baths, through which films must pass in succession. Each bath takes place in a suitably shaped tank containing the treatment liquid. Within each tank, there is a rack of film transport rollers, so distributed within the tank that films are led down one side and back up the other side within the tank, being subjected to the treatment liquid for the duration of their passage through the tank. It is apparent that the larger the tank, the faster the films can be passed through the tank, while still maintaining the durations of treatment periods which are necessary for the various development processes to occur. The same is true for the drying stage, which customarily follows the last bath, and during which the films are subjected to air flow, rather than to a treatment liquid. It is conventional in such machines to have individual gears mounted at the ends of the rollers forming part of the racks. The driving force for each roller is provided through its individual gear.
In the type of transport roller racks here under consideration there is typically a string of many such roller-and-gear assemblies, all of which must be driven from a common power source located at one end of the string, usually near or above the top of the tank within which the respective rack is positioned.
Several techniques for accomplishing this have been utilized.
One technique has involved simply meshing together all the individual roller driving gears with one another, applying the common driving force for all of them to a gear close to the top of the tank, and letting the driving force propagate downwardly along the rack from one gear to another.
This technique has considerable appeal in various respects, and has in fact been widely employed in practice. It follows the accepted principle that a continuous train of gears is simplest to design, assemble and service. It is capable of utilizing mainly one size of gears, which lowers costs and simplifies maintenance. It is susceptible of using the smallest size of gears, which is consistent with the design principle that the smallest possible gears produce a lighter weight and smaller overall package, that the use of small diameter gears minimizes gear cost and results in an optimum gear quality, and that the smaller diameter gears have a lower pitchline velocity and will therefore wear less, last longer and be quieter in action and will give less of a thermal expansion problem.
On the other hand, machines using this technique, with their long series of driven rollers, are beset with the problem of the transmission of power to all these rollers through the corresponding long train of meshing power transmitting gears. For such gear trains, input torque required to overcome friction increases with each added meshing. The difference between the magnitudes of output and input power is attributable to losses due to gear teeth meshing and shaft bearing friction. Such conventional systems show a relatively rapid fall-off of efficiency with length. As shown by conventional systems in use, the number of rollers which can in practice be driven by such a system is severely limited. Also, the play between gear teeth is cumulative with the number of gear meshings, causing objectionable gear chatter, vibration and deflection, all of which increase as the distance from the input power drive increases.
In the case of photographic film processing machines, these defects are critical. They limit the depth of the film treatment tanks, and therefore also the speed with which film can be processed through the machines. Also, they are the cause of damage to the delicate photographic film, the film emulsion can become marked, and the film can show the effect of uneven transport through the system.
A major improvement over the technique described above is taught in the prior applications and issued patent referenced at the beginning of this application. In these prior cases, there is disclosed a system characterized by separation of those gears which transmit the main power along the roller rack from those gears which drive the individual rollers. Power supply, such as a motor, is provided to at least one of these power transmitting gears. The main driving power is transmitted through a plurality of power transmitting gears. From these power transmitting gears, there are tapped off fractions of this main driving power sufficient to drive clusters of gears which, in turn, drive fractions of the total number of transport rollers in the system. The drive from each power transmitting gear to the associated cluster of individual roller-driving gears takes place through a cluster drive gear, which is rotated at the same rate of rotation as the power transmitting gear. Preferably this is accomplished by having the cluster drive gear coaxially connected to the power gear.
Thus, the long train of gears driving the individual rollers in the rack is overbridged by a series of the large power transmitting gears, which are coaxially connected to the smaller cluster drive gears and which drive the long gear train through these cluster drive gears at relatively short intervals. Thus, the long gear train is broken down into a number of smaller clusters of efficiently driven gears, thereby overcoming the multiplying inefficiencies of long gear trains.
As is more fully explained in the above-mentioned prior patent applications and issued patent, the improved system taught therein makes it possible to drive much longer strings of rollers without requiring excessive input driving torque. The system therefore also makes it possible to use much larger tanks. This, in turn, makes possible much higher film processing speeds and output. At the same time, gear chatter and vibration are reduced throughout the system.